Dwan began playing online poker with a $50 bankroll. He initially focused on sit-and-go tournaments, later switching to multiplayer cash games then to heads-up cash games.

According to HighStakesDB.com, a site that tracks high-stakes online poker, Dwan earned $312,800 in 2007 on Full Tilt Poker and $5.41 million in 2008.[5] Before the 2007 World Series of Poker, Dwan claimed to have lost, at the time, $2 million of his $3 million bankroll, over a four month period.[6] He recovered from this loss within a year. In January 2009, Dwan lost more than $3.5 million, which he recovered after six months. However, from late October to late December 2009, Dwan suffered his then largest downswing, losing approximately $2 million to Phil Ivey, Ilari "Ziigmund" Sahamies and $5 million to Viktor Blom.[7]

In mid-November 2009, a player from Sweden using the online name "Isildur1" challenged Dwan to a series of heads-up No Limit Holdem cash games. Isildur1's foray into online high-stakes cash games began in late October, when he initially lost $1.1 million to Patrik Antonius, Brian Townsend, and other high-stakes players. By the beginning of November, Isildur1 had recovered his losses and challenged Dwan to a heads-up marathon playing six tables at a time with over a million dollars in play. By the end of the week, Isildur1 had gone on the largest run in the history of online poker, winning approximately $5 million from Dwan, prompting Dwan to issue a live challenge to play Isildur1 at the Full Tilt Poker Durrrr Million Dollar Challenge.[8]

At the end of 2009, HighStakesDB.com reported that Dwan had lost $4.35 million in 2009, putting his cumulative online poker winnings at Full Tilt since January 2007 at approximately $1.4 million.[9] HighStakesDB.com also reported that after stepping down in limits following his loss to Isildur1, Dwan won $2.7 million in December 2009.[10] According to the same site, Dwan had more than recouped his 2009 losses in the first few months of 2010; he was reported to have won $1.6 million in the first two weeks of April 2010,[11] and after a session in which he won $1.6 million from Sahamies in a little over two hours,[12] was ahead $7.3 million for the year as of April 21.[13] However Dwan lost about $4 million in the next three weeks, leaving him ahead about $3.3 million for 2010.[14]

In January 2009, Dwan issued a $1,000,000 challenge to play anyone online, "with the exception of Phil Galfond", heads up for 50,000 hands four-tabling $200/$400 or higher No-Limit hold 'em or Pot-Limit Omaha. If his opponent is ahead after 50,000 hands, Dwan agreed to give them $1,500,000 more, while if Dwan is ahead, he will get $500,000.[15][16] Regarding his challengers, Dwan has said, "I think all of them actually are better over-all poker players than me -- by quite a bit; I happen to think in this one area, I might have a little edge -- and we'll see if I do."[17]

Patrik Antonius and Daniel Cates are playing Dwan as part of the challenge, but no challenge has been completed. In October 2013, Cates was ahead about $1.2 million after roughly 20,000 hands.[18] Since then, however, Cates has publicly claimed that Dwan has stopped playing and is not responding to his queries.[19]

Dwan was 19 when he cashed in his first live tournament, finishing 12th in the £3,000 no limit Texas Hold 'em Main Event of the European Poker Tour's second season held in London, earning £7,000 ($12,398). His next cash was not until he was 21 years old, at the World Poker Tour's 2007 World Poker Finals $9,700 No Limit Hold 'em Championship Event, where he finished 4th earning $324,244.[20] In January 2008, Dwan finished second at the Aussie Millions A$3,000 Pot Limit Omaha with Rebuys event, winning A$103,200 ($90,716) and later finished in 62nd place in the A$10,000 No Limit Hold 'em Main Event, good for A$25,000 ($21,976).[20] Dwan finished second to James Michael Sowers at the 2008 WPT Borgata Winter Open in the preliminary $5,000 No Limit Hold 'em event, earning $226,100.[20][21]

Dwan cashed twice in the first year that he was eligible to play in a World Series of Poker (WSOP) event held in the United States. Dwan reached the final table in the $10,000 World Championship Mixed Event at the 2008 World Series of Poker finishing in 8th place, earning $54,144. He then nearly made another in a seven person final table, but finished again in 8th, this time in the $5,000 No Limit 2-7 Draw with Rebuys event, earning $45,110.[20]

Dwan holds the record for the largest pot won in a televised live game at over $1.1 million, which occurred during the fourth season of Full Tilt Poker's Million Dollar Cash Game. This record broke the previous record of over $919,000 also won by Dwan in the fifth season of High Stakes Poker.[28]

Dwan's Million Dollar Challenge was expanded to a 500 hand live heads up format in the Full Tilt Poker Durrrr Million Dollar Challenge. The event was held November 17 to 19, 2009, at Les Ambassadeurs Club in London and televised by Sky Sports.

The rules of the Challenge were that each player paid $250,000 for the privilege of playing, blinds were set at $500/$1,000 with each opponent having the choice of playing either Texas hold 'em or Pot Limit Omaha (PLO). Neither player could leave the match until at least 500 hands had been completed or one of them lost all of his buy-in and decided not to re-buy. Dwan's opponents were Marcello "luckexpress" Marigliano, Ilari "Ziigmund" Sahamies, and Sammy "Any Two" George respectively.[29]

The first match between Dwan and Marigliano consisted mainly of Texas hold 'em, although the players did agree to play PLO near the end of the match. Dwan lost $22,500 which was highlighted by two bluffs by Marigliano. In the second match between Dwan and Sahamies the players played only PLO. Although the match started surprisingly slow considering the history of online competition between Dwan and Sahamies, the match eventually became aggressive as expected. There were several large pots resulting in large swings in the players’ stacks. After 12 hours, the match concluded with Dwan winning $68,000.

The final round pitted Dwan against George in an exclusively Texas hold 'em match.[29] During the match, the parties agreed to a 7-2 prop bet wherein if a player wins a pot with 7-2 then he earns an additional $10,000. This led to one of the most memorable bluffs in television poker when Dwan bet $479,500 on the river, all in, into a pot of only $162,000. Dwan was bluffing with 7-2 against George’s two pair (aces and sixes). George folded his two pair after much consideration even though Dwan, after making a 6x pre-flop raise, had said he had 7-2 and just wanted the blinds. George went on to lose $750,000.[29]

Dwan made a final profit of $795,500 after winning two of the three matches.

In November 2009, Dwan became a member of Team Full Tilt and re-signed as a brand ambassador for the site on October 15, 2012.[30][31] In December 2013, Full Tilt Poker confirmed that they and Dwan "agreed to part ways following the recent expiration of Dwan’s contract".[32]